Mixed powder for powder metallurgy

ABSTRACT

Provided is a mixed powder for powder metallurgy that has a low dust generating property and that forms therefrom a compact with high density and enables easy removal of the compact from a forming die. The mixed powder for powder metallurgy in the present invention is characterized by containing an iron-based powder, an auxiliary raw material, and a lubricant, the lubricant being a liquid lubricant that contains an organic metal component.

FIELD OF THE INVENTION

The present invention relates to a mixed powder for powder metallurgy containing an iron-based powder, an auxiliary raw material, and a lubricant, the lubricant being a liquid lubricant containing an organic metal component.

BACKGROUND OF THE INVENTION

Powder metallurgy is conventionally known that uses an iron-based powder to produce a sintered body. In general, the powder metallurgy includes the steps of: mixing an iron-based powder, an auxiliary raw material, and the like; compressing a mixed powder for powder metallurgy obtained in the mixing step by a forming die; and sintering a powder compact obtained in the compressing step (hereinafter referred to as a compact) to below the melting point of the iron-based material, thereby fabricating a sintered body.

In the mixing step, a solid or liquid lubricant is generally known to be added. Among them, known examples of the solid lubricant include ethylene-bis-stearic acid amide, zinc stearate, etc. When intended to remove the compact produced in the compression step from the forming die, the solid lubricant is added to reduce friction resistance between a wall surface of the forming die and the compact, thereby removing the compact from the forming die by a small removing force.

On the other hand, a liquid lubricant is added to further improve the powder properties. For example, in a technique disclosed in Patent Document 1, an organic liquid lubricant, such as an oleic acid, a spindle oil, and a turbine oil, is used together with a solid lubricant. Furthermore, in techniques disclosed in Patent Documents 2 and 3, a drying oil (liquid lubricant) including an ester derived from a multi-polyunsaturated fatty acid and a polyol as well as a desiccant are added, or a drying oil having a viscosity in a specific range is added to improve the powder properties.

RELATED ART DOCUMENT Patent Documents

-   Patent Document 1: Japanese Unexamined Patent Application     Publication No. 2007-2340 -   Patent Document 2: Japanese Translation of PCT International     Application Publication No. JP-T-2008-533298

Patent Document 3: Japanese Translation of PCT International Application Publication No. JP-T-2008-503653

SUMMARY OF THE INVENTION

With the reduced weight of automobiles, sintered parts (especially iron-based sintered parts) have been recently developed to reduce their thickness and weight. However, the reduction in the thickness and weight decreases the strength of the sintered parts. To avoid the decrease in the strength of the sintered part, a compact is required to have higher density. Furthermore, such a compact is also required to have excellent removability from a forming die. On the other hand, a mixed powder for powder metallurgy as a raw material needs to have a low dust generating property in a forming step of the compact. Even the use of the liquid lubricants described in Patent Documents 1 to 3, however, has been found to fail to produce a mixed powder for powder metallurgy that has a low dust generating property and that can form therefrom a compact with high density and enables easy removal of the compact from the forming die.

The present invention has been made in view of the foregoing matter, and it is an object of the present invention to provide a mixed powder for powder metallurgy that has a low dust generating property and that produces therefrom a compact with high density and enables easy removal of the compact from a forming die.

The inventors have found that using a liquid lubricant containing an organic metal component as the lubricant in the mixing step of the powder metallurgy enhances the density of the compact.

That is, a mixed powder for powder metallurgy according to the present invention contains an iron-based powder, an auxiliary raw material, and a lubricant, the lubricant being a liquid lubricant containing an organic metal component.

The lubricant preferably contains at least one of metal salicylates, metal sulfonates, metal phenates, metal thiocarbamates, and metal thiophosphonates.

The lubricant preferably contains, as the organic metal component, at least one of alkali metals, alkaline earth metals, molybdenum, and zinc.

The lubricant is preferably contained in a proportion of 0.01 parts by mass or more and 1 part by mass or less relative to 100 parts by mass of the iron-based powder.

The mixed powder for powder metallurgy in the invention contains the liquid lubricant that contains the organic metal component, whereby the compact formed from the mixed powder has high density and can be removed easily from the forming die. The mixed powder can demonstrate the low dust generating property in the forming step for the compact.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of an instrument for measurement of a graphite scattering ratio in Examples.

DETAILED DESCRIPTION OF THE INVENTION

A mixed powder for powder metallurgy (hereinafter simply referred to as a “mixed powder” in some cases) in the present invention contains an iron-based powder, an auxiliary raw material, and a lubricate; the lubricate is a liquid lubricate that contains an organic metal component. Preferably, the mixed powder for powder metallurgy in the present invention is formed of the iron-based powder, the auxiliary raw material, and the lubricant; the lubricant is preferably a liquid lubricant containing an organic metal component.

<Iron-Based Powder>

The iron-based powder is a raw-material powder containing iron as a principal component, and in other words, is a main raw material of the mixed powder. The iron-based powder may be either a pure iron powder or an iron alloy powder. The term “iron alloy powder” as used herein means a pure ion powder to which an element, such as copper, nickel, chromium, molybdenum, and sulfur is positively added. Note that the iron alloy powder may be a partial alloy powder in which an alloy powder, such as copper, nickel, chromium, or molybdenum, is partially dispersed and attached to the surface of the iron-based powder. Alternatively, the iron alloy powder may be a prealloyed powder obtained from a molten iron or a molten steel that contains an alloy component. The iron-based powder is normally manufactured by performing atomization on a molten iron or steel. The iron-based powder may be a reduced iron powder prepared by reducing iron ore and mill scale.

The mean particle size of the iron-based powder is not limited and may be one that makes the iron-based powder usable as a main raw material for powder metallurgy. For example, the mean particle size of the iron-based powder is 40 μm or more and 120 μm or less. The mean particle size of a metal powder is a particle size at a cumulative undersize amount of 50% when measuring the particle size distribution based on “Standard Test Method for Sieve Analysis of Metal Powder” described in Japan Powder Metallurgy Association Standard JPMA P 02-1992.

<Auxiliary Raw Material>

The above-mentioned auxiliary raw material can be selected as appropriate, depending on the desired properties, and can be arbitrarily determined according to various properties required for end products as long as it does not inhibit the effects of the invention.

Examples of the auxiliary raw material can include metal powders made of copper, nickel, chromium, molybdenum, etc., and inorganic powders made of phosphorus, sulfur, graphite, manganese sulfide, talc, calcium fluoride, etc. These auxiliary raw materials may be contained alone or in combination. The auxiliary raw material preferably contains an inorganic powder, and more preferably contains a graphite powder. The auxiliary raw material in use may be a combination of a metal powder and an inorganic powder, and preferably contains a metal powder and a graphite powder, and most preferably contains a copper powder and a graphite powder.

Such an auxiliary raw material is preferably contained in a proportion of 10 parts or less by mass in total relative to 100 parts by mass of the iron-based powder as the main raw material, more preferably 5 parts or less by mass, and further more preferably 3 parts or less by mass. When the content of the auxiliary raw material relative to the iron-based powder exceeds 10 parts by mass, the density of the compact produced from the mixed powder for powder metallurgy (hereinafter referred to as a compact density) is decreased, which might result in adverse effects, including the reduction in the strength of the sintered body. On the other hand, the lower limit of the content of the auxiliary raw material is not particularly limited, and thus may be, for example, one part or more by mass.

For example, the auxiliary raw materials can be preferably contained in the following ranges. Note that each of the following ranges indicates the content of the auxiliary raw material relative to 100 parts by mass of the iron-based powder.

Copper: 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 1 part by mass or more and 4 parts by mass or less

Graphite: 0.1 parts by mass or more and 3 parts by mass or less, and more preferably 0.2 parts by mass or more and 1 part by mass or less

Nickel: 0.1 parts by mass or more and 10 parts by mass or less, and more preferably 0.5 parts by mass or more and 4 parts by mass or less

Chromium: 0.1 parts by mass or more and 8 parts by mass or less, and more preferably 0.2 parts by mass or more and 5 parts by mass or less

Molybdenum: 0.1 parts by mass or more and 5 parts by mass or less, and more preferably 0.2 parts by mass or more and 3 parts by mass or less

Phosphor: 0.01 parts by mass or more and 3 parts by mass or less, and more preferably 0.05 parts by mass or more and 1 part by mass or less

Sulfur: 0.01 parts by mass or more and 2 parts by mass or less, and more preferably 0.03 parts by mass or more and 1 part by mass or less

Manganese sulfide: 0.05 parts by mass or more and 3 parts by mass or less, and more preferably 0.1 parts by mass or more and 1 part by mass or less

Talc: 0.05 parts by mass or more and 3 parts by mass or less, and more preferably 0.1 parts by mass or more and 1 part by mass or less

Calcium Fluoride: 0.05 parts by mass or more and 3 parts by mass or less, and more preferably 0.1 parts by mass or more and 1 part by mass or less

<Liquid Lubricant>

In the present invention, it is important to use the liquid lubricant containing the organic metal component as the lubricant. When using the liquid lubricant containing the organic metal component, the organic metal component is present at an interface between respective powder particles in the mixed powder, which can enhance the lubricity between the adjacent powder particles. Accordingly, cavities in the compact become fewer, enhancing the compact density. As the density of the compact becomes higher, that is, as the cavities within the compact become fewer, the strength of a sintered body obtained from such a compact becomes higher. On the other hand, when using a liquid lubricant not containing an organic metal component, the lubricity between adjacent powder particles is insufficient, failing to adequately increase a compact density.

The powder used as the auxiliary raw material has a smaller specific weight and a smaller particle size, compared to the iron-based powder as the main raw material, and thus might generate dust in the forming step of the compact, including the above-mentioned mixing step and the compressing step. However, the use of the liquid lubricant containing the organic metal component can enhance the lubricity between the adjacent powder particles, thereby reducing the dust generating properties in the above-mentioned mixing step and compressing step, that is, enhancing the adhesion of the auxiliary raw material to the iron base.

Furthermore, the compact is formed from the mixed powder containing the lubricant used in the present invention, by means of the forming die. Such a compact can be easily removed from the forming die due to the high lubricity between the powder and the wall surface of the forming die and the reduced friction resistance between the compact and the wall surface of the forming die.

The expression “contains an organic metal component” as used in the present invention means that a carbon atom and a metal atom are contained. The organic metal component included in the liquid lubricant preferably contains at least one of alkali metals, alkaline earth metals, and transition metals; more preferably contains at least one of alkali metals, alkaline earth metals, molybdenum, and zinc; further more preferably contains at least one of alkaline earth metals, molybdenum, and zinc; and most preferably contains at least one of calcium, barium, molybdenum, and zinc.

The liquid lubricant preferably contains at least one of a liquid lubricant containing a metal salicylate and a liquid lubricant containing a sulfur atom, and more preferably contains at least one of metal salicylates, metal sulfonates, metal phenates, metal thiocarbamates, and metal thiophosphonates. The liquid lubricant particularly preferably contains at least one of calcium salicylate, calcium sulfonate, and thiocarbamic molybdenum. Calcium salicylate and calcium sulfonate are more likely to be adsorbed in the powder. When using thiocarbamic molybdenum, a lubricant film of MoS₂ is formed near the surface of the powder. The use of such a liquid lubricant tends to enhance its lubricity between the adjacent powder particles, making it easier to re-arrange the powder particles. Thus, the use of calcium salicylate, calcium sulfonate, or thiocarbamic molybdenum reduces the cavities inside the compact, thereby making it possible to further increase the compact density.

As mentioned above, in the present invention, it is important to use the liquid lubricant containing the organic metal component as the lubricant. In addition to the liquid lubricant containing the organic metal component, a solid lubricant or a liquid lubricant not containing an organic metal component may be added.

(Metal Salicylate)

The metal salicylate preferably contains an alkaline earth metal salicylate, and more preferably contains at least one of calcium salicylate and barium salicylate. Examples of the alkaline earth metal salicylate can include alkaline earth metal salts of alkyl salicylic acids. The metal salicylates may be used alone or in combination.

In the alkaline earth metal salicylate, the content of the alkaline earth metal is preferably in a range of 1 to 30% by mass, more preferably 3 to 25% by mass, further preferably 5 to 20%© by mass, and particularly preferably 10 to 15%© by mass.

The alkaline earth metal salicylate may be a commercially available product, for example, trade name M7125, manufactured by INFINEUM (calcium salicylate, calcium content of 12.5% by mass).

(Metal Sulfonate)

The metal sulfonate preferably contains an alkaline earth metal sulfonate, and more preferably contains at least one of a calcium sulfonate and a barium sulfonate. Examples of the alkaline earth metal sulfonate can include alkaline earth metal salts of an alkyl benzene sulfonic acid or an alkyl naphthalene sulfonic acid, which is obtained by sulfonating an alkyl benzene or an alkyl naphthalene, respectively. Metal sulfonates may be used alone or in combination.

In the alkaline earth metal sulfonate, the content of the alkaline earth metal is preferably in a range of 1 to 30% by mass, more preferably 3 to 25% by mass, and further preferably 5 to 20% by mass.

A calcium sulfonate in use may be a commercially available product. Examples of the calcium sulfonate can include ADDITIN®RC4242 (calcium content: 16% by mass), manufactured by LANXESS K.K., and MORESCO Amber®SC45 (calcium content: 2.7% by mass), manufactured by MORESCO Corporation. A barium sulfonate in use may be a commercially available product. Examples of the barium sulfonate can include ADDITIN® RC4103 (barium content: 8% by mass), manufactured by LANXESS K.K., and MORESCO Amber® SB50N (barium content: 6.8% by mass), manufactured by MORESCO Corporation.

(Metal Phenate)

The metal phenate is preferably an alkaline earth metal phenate, and more preferably at least one of calcium phenates and barium phenates. Examples of the alkaline earth metal phenate can include alkaline earth metal salts of alkylphenols and alkylphenol sulfides. Metal phenates may be used alone or in combination.

In the alkaline earth metal phenate, the content of the alkaline earth metal is preferably in a range of 1 to 30% by mass, more preferably 3 to 25% by mass, and further preferably 5 to 20% by mass.

A metal phenate in use may be a commercially available product. Examples of the metal phenate can include Lubrizol6499 (calcium content: 9.2% by mass, and sulfur content: 3.25% by mass), and Lubrizol6500 (calcium content: 7.2% by mass, and sulfur content: 2.6% by mass), manufactured by LUBRIZOL Corporation.

(Metal Thiocarbamate)

The metal thiocarbamate is preferably one represented by formula (1) below:

[R¹R²N—CS—S—]_(a)M^(a)  (1)

where in formula (1), R¹ and R² may be the same or different from each other, and represent a hydrogen atom, an alkyl group or alkenyl group having a carbon number of 1 to 22, or an aryl group having a carbon number of 6 to 22. Note that R¹ and R² are not hydrogen atoms at the same time. M^(a) represents molybdenum, zinc, antimony, copper, nickel, silver, cobalt, lead, tellurium, or sodium. Furthermore, a represents a valence of M^(a).

Examples of the metal thiocarbamates (metal thiocarbamic acid salts) can include molybdenum thiocarbamate (MoDTC), zinc thiocarbamate (ZnDTC), antimony thiocarbamate (SbDTC), copper thiocarbamate (CuDTC), nickel thiocarbamate (NiDTC), silver thiocarbamate (AgDTC), cobalt thiocarbamate (CoDTC), lead thiocarbamate (PbDTC), tellurium thiocarbamate (TeDTC), and sodium dithiocarbamate (NaDTC), preferably, molybdenum thiocarbamate (MoDTC), zinc thiocarbamate (ZnDTC), copper thiocarbamate (CuDTC), and more preferably molybdenum thiocarbamate (MoDTC). Metal thiocarbamates may be used alone or in combination.

MoDTC in use may be a commercially available product. Examples of the MoDTC can include SAKURA-LUBE® 200 (molybdenum content: 4.1% by mass, and sulfur content: 4.6% by mass), SAKURA-LUBE® 165 (molybdenum content: 4.5% by mass, and sulfur content: 5.0% by mass), and SAKURA-LUBE® 525 (molybdenum content: 10% by mass, and sulfur content: 11% by mass), manufactured by ADEKA Corporation.

In the MoDTC, the molybdenum content is preferably in a range of 1 to 20% by mass, more preferably 3 to 15% by mass, and further preferably 7 to 12%© by mass. In the MoDTC, the sulfur content is preferably in a range of 1 to 20%© by mass, more preferably 3 to 15% by mass, and further preferably 7 to 12% by mass.

(Metal Thiophosphonate)

The metal thiophosphonate is preferably one represented by formula (2) below.

[(R³O)(R⁴O)—PS—S]_(b)M^(b)  (2)

where in formula (2), R³ and R⁴ may be the same or different from each other, and represent a hydrogen atom, an alkyl group or an alkenyl group having a carbon number of 1 to 22. Note that R³ and R⁴ are not hydrogen atoms at the same time. M^(b) represents zinc, molybdenum, or antimony. Furthermore, b represents a valence of M^(b).

Examples of the metal thiophosphonate (metal thiophosphoric acid salts) can include zinc dithiophosphate (ZnDTP), molybdenum dithiophosphate (MoDTP), and antimony dithiophosphate (SbDTP), preferably zinc dithiophosphate (ZnDTP), and more preferably zinc dialkyldithiophosphates. Metal thiophosphonates may be used alone or in combination.

ZnDTP in use may be a commercially available product. Examples of the ZnDTP can include ADEKA KIKU-LUBE® Z-112 (zinc content: 7% by mass, and sulfur content: 14% by mass), manufactured by ADEKA Corporation.

In the ZnDTP, the zinc content is preferably in a range of 1 to 20% by mass, more preferably 3 to 15% by mass, and further preferably 5 to 10% by mass. In the ZnDTP, the sulfur content is preferably in a range of 1 to 25%© by mass, more preferably 5 to 20%© by mass, and further preferably 10 to 15% by mass.

Manufacturing methods for the metal salicylates, metal sulfonates, metal phenates, metal thiocarbamates, and metal thiophosphonates are not particularly limited, and can be the well-known manufacturing methods and the like.

The liquid lubricant is preferably contained in a proportion of 0.01 parts by mass or more and 1 part by mass or less relative to 100 parts by mass of the iron-based powder, more preferably 0.1 parts by mass or more and 0.8 parts by mass or less, and further preferably 0.3 parts by mass or more and 0.7 parts by mass or less. When the content of the liquid lubricant is less than 0.01 parts by mass, the sufficient fluidity might not be obtained, whereas when the content of the liquid lubricant exceeds 1 part by mass, the high-density compact might not be obtained because of the excessive content of the liquid lubricant.

<Fabrication Methods of Mixed Powder for Powder Metallurgy, Compact, and Sintered Body>

Now, a description will be given of fabrication methods for the mixed powder for powder metallurgy, the compact, and the sintered body by using the above-mentioned components.

The fabrication method of the mixed powder for powder metallurgy in the present invention involves mixing the auxiliary raw material and the above-mentioned predetermined lubricant with the iron-based powder as the main raw material. The mixing method is not particularly limited, and the well-known mixing methods can be employed. The mixing method preferably involves stirring and mixing, for example, by a mixing tool, such as a mixer, a high-speed mixer, a nauta mixer, a V-blender, or a double cone blender.

Mixing conditions are not particularly limited, and may be those conventionally used in accordance with various conditions, including equipment and production size. Preferably, the mixing conditions are set, for example, such that when using a mixer with blade, the rotation speed of the blade is controlled to be a peripheral speed in a range of approximately 2 m/s or more and approximately 10 m/s or less, and that a mixing time is controlled in a range of approximately 0.5 minutes or more and approximately 20 minutes or less. When using the V-blender or a double-cone mixer, preferably, the mixing conditions are preferably controlled in a range of 2 rpm or more and 50 rpm or less for a mixing time of one minute or more and 60 minutes or less.

The mixing temperature is not particularly limited, but set, for example, at 40° C. or more and 60° C. or less. The mixing temperature is preferably set at 60° C. or lower in terms of the convenience of a heating apparatus. The mixing under such conditions can prepare the mixed powder for powder metallurgy in which various kinds of raw-material powders are homogeneously mixed together.

Then, the above-mentioned mixed powder is used to produce a compact by an ordinary pressure-forming method using a powder compression molding machine. Specific forming conditions are not particularly limited because they depend on the kinds and added amounts of the components contained in the mixed powder, the shape of the compact, the forming temperature of 25° C. or more and 150° C. or less, the forming pressure, and the like. For example, after filling the mixed powder for powder metallurgy in the present invention, into the forming die, the pressure of 490 MPa or more and 686 MPa or less is applied thereto, whereby the compact can be formed.

Finally, the above-mentioned compact is used and sintered by the ordinary sintering method to produce a sintered body. Specific sintering conditions are varied depending on the kinds and added amounts of the components contained in the compact, the types of final products, and the like. However, the compact is preferably sintered at a temperature of 1000° C. or more and 1300° C. or less for 5 minutes or more and 60 minutes or less under an atmosphere of N₂, N₂—H₂, hydrocarbon, etc.

<Compact Density>

In the beginning, 2.0 parts by mass of a copper powder, 0.8 parts by mass of a graphite powder, and 0.5 parts by mass of a lubricant are blended into 100 parts by mass of an iron-based powder to prepare a mixed powder. The mixed powder as a raw material is subjected to press-forming to produce a compact. The theoretical density of the compact is approximately 7.81 g/cm³ (which is the compact density, provided that there is no cavity in the compact). When using the conventional manufacturing method, the upper limit of the compact density is approximately 7.35 g/cm³. However, the use of the liquid lubricant containing the organic metal component can set the compact density at 7.40 g/cm³ or more. The reason for this is that the liquid lubricant used in the present invention tends to spread over between powder particles, compared with a lubricant conventionally used, to sufficiently cover the particle surfaces of the iron-based powder. Thus, the liquid lubricant is supposed to effectively reduce the friction between the powder particles in the compression step of the powder. The compact density is preferably 7.45 g/cm³ or more. Note that specific forming methods for the compact will be described later.

EXAMPLES

Now, the present invention will be described in more detail with reference to examples. However, the present invention is not limited to the examples below, and can be carried out while being appropriately modified within a range that can adapt to the intention described above and below. All these are included in the technical range of the present invention. Evaluation methods used in the examples are as follows.

(1) Graphite Adherability (Adhesion of Graphite to Iron-Based Powder)

The graphite scattering ratio was measured from the content of graphite in the mixed powder before and after the circulation of dried air gas in a factory, whereby the adherability of the graphite was evaluated. As shown in FIG. 1, 25 g of a mixed powder was put into a funnel-shaped glass pipe 2 having an inner diameter of 16 mm and a height of 106 mm equipped with a mesh membrane filter 1 of 10 μm in pore size. N₂ gas at the room temperature was allowed to flow through the gas pipe 2 from its lower side at a flow rate of 0.8 L/min for 20 minutes, and thus the graphite scattering ratio (%) was determined by the following formula. The term “graphite content (%) in the mixed powder” as used in the formula below means the graphite content in percent by mass in the mixed powder. This means that as the graphite scattering ratio is lower, the graphite adherability becomes higher (the dust generating property becomes lower). Note that the graphite content in the mixed powder was determined by quantitative analysis on carbons in the mixed powder using CS-200 (trade name) manufactured by LECO Corporation, which is a carbon-sulfur simultaneous analysis device.

Graphite Scattering Ratio (%)=[1−(graphite content (%) in the mixed powder after the N₂ gas circulation/graphite content (%) in the mixed powder before the N₂ gas circulation]×100

Then, the graphite adherability was evaluated by using the measured graphite scattering ratio based on the following criterion.

A: a graphite scattering ratio of less than 5%

B: a graphite scattering ratio of 5%© or more, and less than 10%

C: a graphite scattering ratio of 10% or more

(2) Compact Density (g/cm³)

The mixed powder, which was used as the raw material, was compacted by a forming die at a pressure of 10 t/cm² at the ordinary temperature (25° C.) to thereby fabricate a columnar compact having Φ25 mm diameter and 15 mm length. In conformity with JSPM standard 1-64 (a metal powder compressibility testing method), the density of the compact fabricated in the way above was measured. The measured compact density was evaluated based on the following criterion.

A: Compact density of 7.45 g/cm³ or more

B: Compact density of 7.40 g/cm³ or more, and less than 7.45 g/cm³

C: Compact density of less than 7.40 g/cm³

(3) Removal Pressure (MPa)

A removal pressure was determined by dividing a load that was required to remove the obtained compact from the forming die when measuring the compact density (2), by a contact area between the forming die and the compact. The measured removal pressure was evaluated based on the following criterion.

A: Removal Pressure of less than 35 MPa

B: Removal Pressure of 35 MPa or more

Example 1

A pure iron powder having a particle size of 40 μm or more and 120 μm or less (“Atmel 300M” manufactured by KOBE STEEL Ltd) was prepared. To 100 parts by mass of this pure iron powder, 2.0 parts by mass of a copper powder and 0.8 parts by mass of a graphite powder were added and mixed together by a V-blender, thereby producing a mixture. Then, calcium salicylate (M7125, manufactured by INFINEUM, and having a calcium content of 12.5% by mass) was added as a liquid lubricant to the mixture, and blended by using the V-blender, thereby producing a mixed powder for powder metallurgy. At this time, the liquid lubricant was controlled to be 0.50 parts by mass relative to 100 parts by mass of pure iron powder. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Example 2

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of calcium salicylate as the liquid lubricant, calcium sulfonate (ADDITIN® RC4242, manufactured by LANXESS K.K., and having a calcium content of 16% by mass) was added. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Example 3

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of calcium salicylate, barium sulfonate (ADDITIN® RC4103, manufactured by LANXESS K.K., and having a barium content of 8% by mass) was added as the liquid lubricant. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Example 4

In this example, a mixed powder for powder metallurgy was produced in substantially the same way as that in Example 1 except that in place of calcium salicylate, molybdenum dialkyldithiocarba mate (ADEKA SAKURA-LUBE® 525, manufactured by ADEKA Corporation, and having a molybdenum content of 10% by mass and a sulfur content of 11% by mass) was added as the liquid lubricant. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Example 5

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of calcium salicylate, zinc dialkyldithiophosphate (ADEKA KIKU-LUBE® Z-112, manufactured by ADEKA Corporation, and having a zinc content of 7% by mass and a sulfur content of 14% by mass) was added as the liquid lubricant. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Comparative Example 1

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of calcium salicylate as the liquid lubricant, a polyol ester for lubricating oil (UNISTAR® HP-281R, manufactured by YUKA SANGYO Co., Ltd) was added. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Comparative Example 2

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of calcium salicylate as the liquid lubricant, an ester for lubricating oil (UNISTAR® M-182A, manufactured by YUKA SANGYO Co., Ltd) was added. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Comparative Example 3

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of calcium salicylate as the liquid lubricant, a complex ester (UNISTAR® TOE-500, manufactured by YUKA SANGYO Co., Ltd) was added. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Comparative Example 4

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of the liquid lubricant, ethylene-bis-stearic acid amide, which was a solid lubricant, was added. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

Comparative Example 5

In this example, a mixed powder for powder metallurgy was produced in the same way as that in Example 1 except that in place of the liquid lubricant, zinc stearate, which was a solid lubricant, was added. Various types of evaluations were performed on such a mixed powder by the above-mentioned evaluation methods. The results of the evaluations are shown in Table 1 below.

TABLE 1 Graphite adherability Graphite Compact density Removal pressure Lubricant scattering ratio Evaluation (g/cm³) Evaluation (MPa) Evaluation Example 1 Calcium salicylate 0% A 7.45 A 30 A Example 2 Calcium sulfonate 0% A 7.45 A 27 A Example 3 Barium sulfonate 0% A 7.40 B 27 A Example 4 Molybdenum dialkyldithiocarbamate 0% A 7.45 A 30 A Example 5 Zinc dialkyldithiophosphate 0% A 7.40 B 27 A Comparative Polyol ester for lubricating oil 0% A 7.35 C 32 A Example 1 Comparative Ester for lubricating oil 0% A 7.35 C 32 A Example 2 Comparative Complex ester 0% A 7.35 C 32 A Example 3 Comparative Ethylene-bis-stearic acid amide 5% B 7.35 C 27 A Example 4 Comparative Zinc stearate 5% B 7.35 C 30 A Example 5

Based on the results shown in Table 1, the following consideration can be made.

The compacts formed from the mixed powders in Examples 1 to 5 that used the liquid lubricants containing the organic metal components had a high density and could be easily removed from the forming die. In the forming step of the compact, the graphite adherability of each of the mixed powder was high. On the other hand, in Comparative Examples 1 to 3 that used the liquid lubricants not containing the organic metal components, the compact density did not become sufficiently high. In Comparative Examples 4 and 5 that used the solid lubricants, the graphite adherability in the forming step of the compacts was inferior while the compact density did not become sufficiently high.

The mixed powder for powder metallurgy in the present invention uses, as the lubricant, the liquid lubricant containing the organic metal component, whereby the compact formed from the mixed powder has the high density and can be removed easily from the forming die. Furthermore, the mixed powder had the low dust generating property in the forming step of the compact. Therefore, the sintered body formed from the mixed powder for powder metallurgy in the invention has the sufficient strength even though it was reduced in thickness and weight. Thus, the sintered body can be used as a complicated thinned part. 

1. A mixed powder for powder metallurgy, comprising: an iron-based powder; an auxiliary raw material; and a lubricant, the lubricant being a liquid lubricant that contains an organic metal component.
 2. The mixed powder for powder metallurgy according to claim 1, wherein the lubricant contains at least one selected from the group consisting of metal salicylates, metal sulfonates, metal phenates, metal thiocarbamates, and metal thiophosphonates.
 3. The mixed powder for powder metallurgy according to claim 1, wherein the lubricant contains, as the organic metal component, at least one selected from the group consisting of alkali metals, alkaline earth metals, molybdenum, and zinc.
 4. The mixed powder for powder metallurgy according to claim 1, wherein the lubricant is contained in a proportion of 0.01 parts by mass or more and 1 part by mass or less relative to 100 parts by mass of the iron-based powder.
 5. The mixed powder for powder metallurgy according to claim 2, wherein the lubricant contains, as the organic metal component, at least one of alkali metals, alkaline earth metals, molybdenum, and zinc.
 6. The mixed powder for powder metallurgy according to claim 2, wherein the lubricant is contained in a proportion of 0.01 parts by mass or more and 1 part by mass or less relative to 100 parts by mass of the iron-based powder.
 7. The mixed powder for powder metallurgy according to claim 3, wherein the lubricant is contained in a proportion of 0.01 parts by mass or more and 1 part by mass or less relative to 100 parts by mass of the iron-based powder.
 8. A mixed powder comprising: an iron-based powder; an auxiliary raw material; and a lubricant, the lubricant being a liquid lubricant that contains an organic metal component. 